Flammable vapor detector



Sept. 1, '1959 2,902,682

E. J. JOHNSON ETAL FLAMMABLE VAPOR DETECTOR Filed Au 27, 1956 2 Sheets-Sheet 1 mam/2m l'd gar'JJo'hzian gym; llf' ireem Sept. 1, 1959 Filed Aug. 27, 1956 E. J. JOHNSON ET AL FLAMMABLE VAPOR DETECTOR .2 Sheets-Sheet 2 lA/l/ENM/E? Z arifolzrwan nil fires.

United States Patent C) FLLE VAPOR DETECTOR Edgar J. Johnson and Milton W. Green, Princeton,.N.J.,

assignors to Radio Corporation of America, a corporation of Delaware Application August 27, 1956, Serial No. 606,306

9 Claims. (Cir 340237) Our invention relates to apparatus for the detection of flammable vapors and gases in confined spaces.

The presence of flammable vapor in confined spaces creates a hazard of explosion or fire. This hazard, in the past, has caused much loss of life and property. A particular example of the hazard exists in the use of gasoline for powering motor boats. Gasoline vapors often accumulate in the bilges of a boat and become ignited by an electrical spark or from other causes.

Among the objects of our invention are the following: to provide a flammable vapor detector of simple construction capable of extended use without adjustment; to provide a flammable vapor detector which can produce a strong positive actuation of an indicator device to warn of the presence of flammable vapor; to provide a flammable vapor detector whose operation is unaffected by changes in ambient temperature; and, to provide a flammable vapor detector in which no delicate electronic circuitry is needed for the actuation of a warning device.

We have found that we can devise a flammable vapor detector which achieves these objects through the combined use of a magnetic body and a reaction-initiating element. Preferably the reaction-initiating element is a heating element which we place in the vicinity of the body and use to oxidize a small sample of flammable vapor without igniting the entire volume in the confined space being tested. When flammable vapor is oxidized by the heating element, heat is liberated raising the temperature of the magnetic body. As the temperature of the body is raised through its Curie-point the magnetic susceptibility of the magnetic body is suddenly reduced from a near maximum value to a minimum value. This'virtually amounts to complete destruction of the magnetic field of the body. We use the destruction of the magnetic field to actuate an indicator device to give warning of the presence of flammable vapor. In one embodiment of our invention, we use a relay-type of structure in which oxidation of flammable vapor causes an armature to spring away from a magnetic core and actuate a warning device. In another embodiment, we use a transformer type structure, in which oxidation of flammable vapor causes a cut-olt of induced signal in a secondary winding to actuate a warning device.

In the drawings:

Fig. 1 illustrates, partly in cross section and partly in schematic representation, a relay-type of flammable vapor detector constructed in accordance with our invention, and Fig. 2 schematically illustrates a transformer-type of flammable vapor detector constructed in accordance with our invention.

The general assembly of the relay-type detector is shown in Fig. 1 in combination with an example of a utilization circuit which can be actuated by the detector. The actuating portion of the detector comprises a magnetic core 11, a heating coil 12, and an armature 1 3'. though a permanent magnet can be used for the core' 11', we prefer to use anelectromagnet. The heating coil 12 is mounted on the core 11 between the electromagnetic ener- 7 2,902,682 Patented Sept- 1, 1959 ice gizing coil 14 and the armature 13. The armature 13 is spring biased so that it-will spring away from the core 11 when it is not magnetically attracted thereto. Energizing current is supplied to the energizing coil. 14 and heating current to the heating coil 12 by circuitry which will be described hereinafter.

When no flammable vapor is in contact with the heating coil 12, the core 11 is magnetically energized and attracts the armature 13 to it. When flammable vapor comes into contact with the heating coil 12 the vapor is oxidized, liberating heat which raises the temperature of the core 11; As the rising temperature of the core 11 passes through its Curie-point the core s'uddenly loses its magnetic holding power permitting the armature 13 to spring away from the core 11. We use this movement oi the armature 13 to actuate a switching arrangement control: ling a warning device. In order to provide for optimum performance, it is preferable that the heating coil 12 comprise material catalytic to the oxidation of flammable vapor rather than material which must be operated at its glow temperature to oxidize the vapor. When the heating coil 12 is made of catalytic material it can be operated at a temperature Well below giow temperature. Operation of the heating coil 12 at this lower temperature constitutes one of the safety factors' which we have incorporated in the preferred embodiments of our invention to prevent malfunctioning of the flammable vapor detectorfrom causing an explosion. The use of catalytic material also provides certain operational advantages. Less current is required than would be the case if'the heating coil 12 were operated at glow temperature. Also, operation of the heating coil 12 at the lower temperature substantially increases its operational lite. Examples of suitable catalytic materials include platinum, paladium, osmium, and rhodium. We have found that platinum wire and platinum coated wire are readily obtainable and that they provide reliable and eflicient performance. When platinum or platinum coated wire is heated to a temperature of C. or above it becomes a very sensitive catalyst and promotes rapid oxidation of flammable vapor. Such wire can be maintained at temperatures above 85 C., but below glow temperature (about 425 C.)', for long periods of time without any detectable physical deterioration of the Wire.

The core 11 can be made from many suitable ferrites and ferromagnetic materials. Ferrites have one advantage over other magnetic materials in that the heating coil 12 can be wound directly on the core 11 without the interposition of any electrical insulation between the two; Since the core 11 and the heating coil 12 must cooperate to produce the desired result, the selection of material for one depends, to a large extent, on the operational characteristics of the other. Operation of the catalytic heating coil 12 at a sensitizing temperature of 85 C. or above requires that a magnetic material be chosen having a Curiepoint' above the temperature at which the heating coil12 is operated. Because it is desirable to operate the heating coil 12 at a temperature Well below its glow temperature, the magnetic material should be chosen to have a Curiepoint which is also below glow temperature. consideration must also be given to the effects of ambient temperature changes. The Curie-point of the chosen magnetic material should be sufficient'ly' abovetthe operating temperature of the heating coil 12 so that a rise in ambient temperature cannot produce a false indication of the resence of flammable vapor. Excellent results can be achieved by using in combination a core 11 of ferrite having a Curie-point in the vicinity of 350 C. and a heating coil 12 of S-mil platinum coated Wire operated within a temperature range of from C. to 250C. in thea'bsence of'flammable vapor. We have used these materials and, in response to flammable vapor contacting the heating coil 12, have produced a substantially complete collapse of the magnetic field of the core 11 in as little as 8 seconds.

As a safety measure the actuating unit of the detector the familiar Davy-lamp enclosure. A practical enclosure can be constructed as an open-ended box having sides 21 of heat-conductive material such as copper. Across each open end of the enclosure are multiple screens 22 made of several layers of fine wire gauze (preferably copper) with air spaces between layers. The screens 22 permit flammable vapor to permeate the enclosure to contact the heating coil 12. At the same time, the heat conductive properties of the screens 22 and the sides 21 are such that heat generated Within the small volume of the enclosure during the oxidation of flammable vapor is dissipated by the screens 22 and the sides 21 before it can ignite flammable vapor in the atmosphere surrounding the safety enclosure. 7 To illustrate the utility of this embodiment of our invention we have included in Fig. 1 an electrical network suitable for use in motor boats. The network includes circuitry for supplying current to the energizing coil 14 and the heating coil 12. It also includes circuitry controlled by the actuating unit of the detector for selectively actuating a warning indicator 31 and a safe-operation indicator 41, both being shown as incandescent lamps.

The energizing coil 14 and the heating coil 12 are supplied with current by a battery 51. The current path from the battery 51 includes a main switch 52, a fuse 53, a variable resistance 54, an insulated connector 55, the energizing coil 14, and the heating coil 12, all connected in series. From the heating coil 12 a path back to the battery 51 is provided over two parallel circuit branches. The main branch includes an upper armature-controlled switch 42 (shown as a push button for the purpose of illustration), a lead 56 to a connector 57 in one of the sides of the enclosure and a lead 58 from the connector 57 back to the battery 51 A bypass branch, around the upper switch 42, includes a lead 45 from one pole of the switch 42 to an insulated connector 44 in the side of the enclosure. From this insulated connector 44 a current path is provided by another lead 43 to a push button contact maker 46, and by a third lead 47 from the push button 46 back to the battery 51.

Closing the main switch 52 does not initiate operation of the energizing circuit. At the instant the main switch 52 is closed the energizing coil 14 has no current flowing through it and there is no magnetic field induced in the core 11. In the absence of a magnetic field, the spring bias of the armature 13 will hold it away from the core 11, and the upper switch 42 in the energizing circuit will be open. While this switch 42 remains open, no current can flow back to the battery 51 through the main circuit branch. At the s ame time, since the contacts of the push button 46 are unconnected, no current can flow back to the battery 51 through the bypass circuit branch.

After the main switch 52 is closed, circuit operation is initiated by depressing the push button 46. Connecting the contacts of the push button 46 allows current to flow from the battery 51 through the energizing coil 14, the heating coil 12, and through the bypass branch of the circuit back to the battery 51. As soon as current flows through the energizing coil 14 a magnetic field is induced in the core 11. The magnetic field attracts the armature 13 to the core 11, closing the upper switch 42. Once the switch 42 has closed the push button 46 can be released to open the bypass branch. Opening of the bypass branch will not interrupt current flow through the energizing coil 14 since, with switch 42 closed, current can now flow back to the battery 51 through the main branch.

Current flow through the heating coil 12 requires a finite length of time in which to bring the heating coil 12 and the core 11 up to operating temperature. The time required will vary depending upon the voltage of the battery 51 and upon the ambient temperature but, under normal conditions, should not exceed 6 to 8 seconds. The variable resistance 54 is included in the energizing circuit to regulate the current flowing through the heating coil 12. Once the heating coil current has been adjusted to obtain an appropriate operating temperature, no further adjustment of the variable resistance 54 should be required during normal operation.

In the absence of flammable vapor, the energizing circuit will continue to operate as described above. With flammable vapor in the enclosure initially or when it permeates the enclosure to come in contact with the heating coil 12, oxidation of the vapor results. When this is the case the temperature of the heating coil 12 rapidly rises to a value which is in excess of the Curiepoint of the core 11. The temperature of the core 11 rises in a corresponding manner and, when the Curiepoint is reached, the core 11 loses its magnetic holding power. At this instant, the armature 13 springs away from the core 11, opening the upper switch 42. This interrupts the current flowing through the energizing coil 14, the heating coil 12, and the main branch back to the battery. Note that this cuts off the current flow through the heating coil 12 before it reaches glow temperature, and thus an additional safety factor is provided to further prevent malfunctioning of the flammable vapor detector from causing an explosion. Once the actuating unit of the detector has been triggered in response to the presence of flammable vapor, current will not again flow through the energizing circuit until the push button 46 in the bypass branch is depressed.

The warning indicator 31 is connected to the battery 51 through the main switch 52. From the warning indicator 31 a lead 33 ms to an insulated connector 34 through one of the sides of the safety enclosure. Another lead 35 runs from this connector to one pole of a lower armaturecontrolled switch 32 (also shown as a push button); and, a third lead 36 from the other pole of this switch 32 ties in with the main branch of the energizing circuit at the connector 57 in that branch. Thus, when the main switch 52 and the lower switch 32 are closed, current will flow in the circuit to actuate the warning indicator 31.

As was described with regard to the energizing circuit, closing the main switch 52 does not energize the core 11, and the armature 13 remains spring biased away from the core 11. When the armature 13 is in this position the lower switch 32 is closed and the warning indicator 31 actuated. As soon as the push button 46 is depressed the armature 13 is attracted to the core 11, opening the lower switch 32 to de-energize the warning indicator 31. When flammable vapor permeates the safety enclosure it causes the armature 13 to close the lower switch 32 and again actuate the warning indicator 31. The warning indicator 31 will remain actuated until the push button 46 is depressed or until the main switch 52 is opened to de-energize the entire apparatus.

The safe-operation indicator 41 (of any desired type, but show and referred to illustratively as an incandescent lamp) is connected to the battery 51 through the main switch 52 and a time-delay device 40. The indicator lamp 41 is connected by means of the lead 43, the insulated connector 44 and the lead 45 (all in the bypass branch of the energizing circuit) to the same pole of the upper switch 42 as in the heating coil 12. From the other pole of the upper switch 42 the circuit path for the safe-operation indicator 41 follows the main branch of the energizing circuit back to the battery 51. The time delay device 40 is included to prevent actuation of the safe-operation indicator until suflicient time has elapsed for the detector to have actuated the warning indicator 31 if flammable vapor was present. A convenient means for obtaining an appropriate time delay is to combine in series circuit an incandescent lamp (the safe-operation indicator 41) and a resistor having a negative resistance-temperature characteristic. Many such resistors are commercially available, one type being known in the trade as a thermistorfi The time delay which can be achieved in this mannerdepends upon the change in resistance of both the incandescent lamp and the thermistor in progressing from cold to hot operation. By properly matching the two a-convenient delay, such as 30 seconds, can be produced. Using a thermistor to obtain time-delay gives another advantage. When the detector is used' under conditions where battery voltage might decrease so as to increase the time required for the heating coil 12 to attain its operating temperature, the thermistor will produce a correspondingly longer time-delay before actuation of the safeoperation indicator lamp 41.

Current flows through the circuit which includes the lam 41 and the thermistor 40' upon the closing: of the upper armature-controlled switch 42. Current flowing through the" thermistor 40 gradually heats it up until its resistance drops to a level which permits the lamp 41 to light up and serve as a safe-operation indication. If any flammable vapor is present, thefarmature 13 will have had suflicient time to actuate the circuit of the warning indicator 31 and at the same time open both the energizing circuit and the circuit of the safe-operation indicator 41. Thus, no false safe indication will ever be produced when a dangerous condition exists.

' A flammable vapor detector constructed in accordance with this embodiment of our invention provides a boat operator with a valuable monitor which conduces to safe boating. When a-boat operator closes the main switch 52 (which might well occur simultaneously with the turning on of the boats ignition switch), actuation of the warning indicator 31 informs him that the flammable vapor detector is in condition to perform its function. When he then depresses the push button 46, de-energiza tion of the warning indicator 31 informs him that his detector is performing its function and will, after a brief time delay, tell him whether or not flammable vapor is present. If, after this time delay, the warning indicator 31 again comes on the boat operator knows that a condition exists wherein it would be dangerous for him to start his motor. If, instead, the safe-operation indicator comes on he knows it is safe to start the motor.

The flammable vapor detector is not limited to providing a safety check before getting under way. It also functions to provide continuous monitoring during a voyage. Should a gasoline leak develop while under way, the detector will promptly warn the operator to institute remedial measures.

In Fig. 2 is shown the general assembly of a transformer type of flammable vapor detector. Its actuating unit comprises a magnetic core 60,21 primary winding 61 and a secondary winding 62 on the core 60, and a heating coil 12 disposed on a portion of the core 60 intermediate the primary and secondary windings. Also included in Fig. 2 is a circuit network identical in most respects to the network of the embodiment of Fig. 1. This notwork and the manner in which it is controlled by the actuating unit of the detector will be described hereinafter.

Operation of this embodiment of our invention requires that an alternating or pulsing current suitable for transformer excitation be fed through the primary winding 61. This current induces an alternating magnetic field in the core 60. As long as no flammable vapor comes in contact with the heating coil 1-2", the alternating magnetic field will induce an alternating current signal in the secondary winding 62. When flammable vapor contacts the heating coil 12., oxidation of the vapor raises the temperature of the core 60 through its Curiepoint. When this happens, the magnetic susceptibility of the core 66 is suddenly reduced to a minimum, sharply cutting off the signal induced in the secondary winding 62. This cut-off signal is used to actuate a warning indicator.

As was the case in the embodiment of Fig. 1, the actuating unit of this embodiment also is mounted in a safety enclosure (illustrated by the dashed line .10). The ma- '6 terials comprising the core 60' and the heating coil 12 have; the same characteristics as those comprising the core 11 and the heating coil 12 in Fig. 1.

v In Fig. 2, control of the circuit network is'accomplished by including in series circuit with the secondary winding 62 an alternating current relay 63 whose armature 64 is in circuit with the elements of the network. Alternating or pulsing current from a source 51' starts flowing in' the primary winding when the push button 46 is depressed with the main switch 52 closed. The signal derived from the secondary winding 62 will energize the relay 63, moving its armature 64 away from one terminal 65 to contact a second terminal 66. Initially the armsture 64 completed the circuit between the warning indicato'r 31 and the source of current 51' to actuate the warning indicator 31. When the armature 64 moved away from the terminal 65 it de-e'nergiz'edthe warning indicator 3;. Contact of the armature 64 with the second terminal 66 provides an alternate path for the current through the primary winding 61 to return to the source 51' so that release of the push button 46 will not interrupt this current flow. This alternate path includes the terminal 66, the armature 64, and the main branch lead 58 back to the source 51'. Contact ofthe armature 64 with the second terminal 66 also starts current flowing in the circuit of the safe-operation indicator 41. :This latter current flow, in the absence of flammable vapor, will actuate the safe-operation indicator subject to the time delay produced by the thermistor 40;

When flammable vapor is oxidized by the heating coil 12 this cuts off the signal induced in the secondary winding 62., and the relay 63 is de-energized. When this happens, the armature 64 springs away from terminal 66 and contacts the other terminal 65. This movement of the armature de-en'ergizes both the circuit of the safe- Warning indicator 41 and the energizing for the primary winding 61. It also closes the circuit of the warning in dica'tor 31 to actuate that device. Once the relay 63- has been de-energized in response to the presence of fiammable vapor, current will remain cut oif in the energizing circuit and in the circuit the safe-operation indicator 41 but will continue to flow in the circuit of the warning indicator 31. This condition of current flow in the circuit network can only be changed by depressing the push button 46, or by opening the main switch 52 to de-energize the entire apparatus.

What'we claim as our invention is:

1. A flammable vapor detector adapted to open and close an electrical indicator circuit, said detector compris mg a body of magnetic material, a reaction-initiating ele-' ment for oxidizing flammable vapor at the vicinity of said body, and a switching device associated with said body and'responsive to the condition of magnetic susceptibility of said body, said switching device including electrical contacts adapted for connection of said indicator circuit thereto, said switching device being responsive to substantially' minimum susceptibility in said body to close said contacts and responsive to substantially maximum susceptibility in said body to open said contacts.

2. The device of claim 1 in which the magnetic material is chosen to have a Curie-point intermediate the temperature imparted to said body of magnetic material by the reaction-initiating element in the absence of flammable vapor and the temperature imparted to said body as a result of the oxidation of flammable vapor.

3. The device of claim 1 in which the reaction-initiating element is a heating element comprising material catalytic to the oxidation of flammable vapor at a temperature well below its glow temperature.

4. The device of claim 1 in which said switching device comprises a relay-type armature disposed adjacent tosaid body so as to be linked by the magnetic field thereof, and in which there is provided means for inducing a magnetic field in said body.

5. The device of claim 1 in which the body of magnetic material comprises a transformer-type core, and has associated with it means for inducing a changing magnetic field in said body.

6. A flammable vapor detector comprising a magnetic core; an energizing winding on said core; a heating coil surrounding a portion of said core, the surface of said heating coil comprising material catalytic to the oxidation of flammable vapor at a temperature well below glow temperature; said core comprising magnetic material chosen to have a Curie-point intermediate the temperature imparted to said core by said heating coil in the absence of flammable vapor and the glow temperature of said heating coil; electrical switching means associated with said core and actuated to a first switching position in response to a minimum of magnetic susceptibility of said core and actuated to a second switching position in response to substantially maximum magnetic susceptibility of said core; a pair of electrical terminals adapted for the connection of a source of current thereto; a first circuit connected to said terminals and including said energizing winding and said heating coil, said switching means completing said first circuit when actuated to said second switching position, a manually operated contact maker in said first circuit in parallel with said switchng means; a second circuit connected to said terminals and including a Warning indicator, said switching means completing said second circuit when actuated to said first switching position; a third circuit connected to said terminals and including a safe-operation indicator, delay means associated with said safe-operation indicator to delay the indication thereof for a time at least equal to the time required for the oxidation of flammable vapor to raise the temperature of said core to its Curie-point, said switching means completing said third circuit when actuated to said second switching position; and an enclosure for at least said heating coil, at least a portion of said enclosure comprising heat-conductive safety-screen material.

7. A flammable vapor detector comprising a magnetic core; an energizing coil on a portion of said core; a relaytype armature disposed in magnetically attractable relation to said core, said armature having a spring bias to impel it away from said core in the absence of magnetic attraction thereto; a first switching means disposed relative to said armature to make electrical contact when said armature is magnetically attracted to said core; a second switching means disposed relative to said armature to make electrical contact when said armature is impelled away from said core; a heating coil on said core intermediate said armature and said energizing coil, the surface of said heating coil comprising material catalytic to the oxidation of flammable vapor at a temperature well below its glow temperature; said core comprising magnetic material chosen to have a Curie-point intermediate the temperature imparted to it by said heating coil in the absence of flammable vapor and the temperature imparted to it as a result of the oxidation of flammable vapor; a pair of electrical terminals adapted for the connection thereto of a source of current; a first circuit connected to said terminals and including said energizing coil, said heating coil, said first switching means, and current adjusting means, said first circuit also including a manually operated contact maker in parallel with said first switching means; a second circuit connected to said terminals and including a warning indicator and said second switching means; a third circuit connected to said terminals and including a safe-operation indicator and said first switching means, a time delay device associated with said safe-operation indicator to delay the indication thereof for a time at least equal to the time required for the oxidation of flammable vapor to raise the temperature of said core to its Curie? point; and an enclosure for at least said heating coil, at least a portion of said enclosure comprising heat-conductive safety-screen material.

8. A flammable vapor detector comprising a magnetic core; a primary winding on said core; a secondary winding on said core; a heating coil on said core intermediate said primary and secondary windings, at least the surface of said heating coil comprising material catalytic to the oxidation of flammable vapor at a temperature well below its glow temperature; said core comprising magnetic material chosen to have a Curie-point intermediate the temperature imparted to it by said heating coil in the absence of flammable vapor and the temperature imparted to it by the oxidation of flammable vapor; an alternating current relay connected in series with said secondary winding and having an armature; first switching means disposed relative to said armature to make electrical contact when said relay is energized; second switching means disposed relative to said armature to make electrical contact when said relay is de-energized; a pair of electrical terminals adapted for the connection thereto of a source of current; a first circuit connected to said terminals and including said energizing coil, said heating coil, said first switching means, and current adjusting means, said first circuit also including a manually operated contact maker in parallel with said first switching means; a second circuit connected to said terminals and including a Warning indicator and said second switching means; a third circuit connected to said terminals and including a safe-operation indicator and said first switching means, a time delay device associated with said safe-operation indicator to delay the indication thereof for a time at least equal to the time required for the oxidation of flammable vapor to raise the temperature of said core to its Curie-point; and an enclosure for at least said heating coil, at least a portion of said enclosure comprising heat-conductive safety-screen material.

9. A flammable vapor detector comprising a body of magnetic material, a reaction-initiating element for oxidizing flammable vapor at the vicinity of said body, an electrical indicator circuit having a first portion thereof associated with said body and responsive to the condition of magnetic susceptibility of said body, a second portion of said indicator circuit actuated by said first portion to become energized in response to substantially minimum susceptibility of said body to provide an indication indicative of the presence of flammable vapor, and a third portion of said indicator circuit actuated by said first portion to become energized in response to substantially maximum susceptibility of said body to provide an indication indicative of the absence of flammable vapor, said third portion of said indicator circuit including means for delaying its indication a time at least equal to the time required for the temperature of said body to be raised to its Curie-point by the oxidation of flammable vapor.

References Cited in the file of this patent UNITED STATES PATENTS 2,255,638 Armstrong Sept. 9, 1941 2,339,125 Winter Jan. 11, 1944 2,535,950 Page Dec. 26, 1950 2,540,527 Ingels Feb. 6, 1951 2,784,355 Van Suchtelen Mar. 5, 1957 UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 2,962,682

Edgar 5., Johnson et a2.

It is hereby certified that error appears in the printed specification of the above numbered patent requiring correction and that the said Letters Patent should readas corrected below.

Column 3, line 4, after "detector" insert ad is mounted. within a safety enclosure patterned after column 4, line for "show" read. shown Signed and sealed this 1st day of 196G E Attest:

KARL Ha AXLINE Attesting Ofiicer ROBERT C. WATSON Commissioner of Patents 

